While the problems of fire and of fragments can be solved in practice with the aid of traditional compound explosives, the problem of sympathetic detonation, more precisely of vulnerability to the nearby detonation of neighboring munitions, has not yet been solved in a satisfactory manner. It is well known to employ plastic bonded explosives, especially cast plastic bonded explosives of particularly low sensitivity filled, for example, with 5-oxo-3-nitro-1,2,4-triazole (ONTA), with triaminotrinitrobenzene (TATB) or nitroguanidine. However, this solution has a major disadvantage, namely that the vulnerability of the munition to nearby detonation of neighboring munitions is then dependent on that of the initiation system. Now, these low-sensitivity plastic bonded explosives generally have a large critical diameter which may exceed 10 cm, and can be initiated conventionally only by a powerful relay of large size, and therefore particularly sensitive and vulnerable.
A plastic bonded explosive is conventionally intended to mean a pyrotechnic composition capable of being functionally detonated, consisting of a filled solid polymeric matrix, generally filled polyurethane or polyester, the filler being pulverulent and containing an organic nitrated explosive charge, for example Hexogen, Octogen, ONTA or a mixture of at least two of these compounds. The cast plastic bonded explosives and the manner in which they are obtained are described, for example, by J. Quinchon, "Les poudres, propergols et explosifs" [Powders, propellants and explosives], volume 1, Les explosifs, Technique et Documentation, 1982, pages 190-192.
French Patent FR 2,365,774 describes an approximately cylindrical component of explosive munition, consisting of a casing containing a multicomposition charge which may be a plastic bonded explosive. This multicomposition charge comprises a plurality of adjacent coaxial annular layers, the peripheral layer having a content of powerful heavy explosive (Hexogen, Octogen) which is higher than that of the layer immediately adjacent to it and thus step by step until the central axial layer, which is fully cylindrical, and, comprises the lowest content of powerful heavy explosive. Such an explosive munition component is therefore particularly vulnerable.
Furthermore, the article "Insensitive Munitions-A fire safety plus?" which appeared in May 1989 in the review "Military Fire Fighter" pages 74 to 81, teaches that the vulnerability of a munition component filled with sensitive plastic bonded explosive can be reduced by coating this explosive with a less sensitive plastic bonded explosive, the twin-composition charge being in the form of 2 adjacent coaxial cylinders with a circular base surface.
The less sensitive plastic bonded explosives are, however, less effective and the reduction in the vulnerability of the munition component is accompanied by a drop in performance. Experimental tests carried out by the applicants, forming the subject of Comparative Examples 3 to 5 of the present description, have even shown that the fragmentation effect of such a munition component could be reduced to the level of that obtained with a munition component of the same size but filled solely with the less vulnerable and less effective coating plastic bonded explosive.
The person skilled in the art seeks therefore an improvement in relation to this munition component comprising a dual-composition charge which makes it possible to increase the fragmentation effect while maintaining the same degree of invulnerability.
The present invention proposes such a solution.
It has been found, unexpectedly, that if the interface between the two compositions, along a cross-section in relation to the axis of the charge, is in the shape of a star, instead of being circular as according to the state of the art, a gain, sometimes very large, is obtained in the fragmentation effect and that, according to certain alternative forms --which is even more surprising--the degree of fragmentation effect obtained is equal to that obtained with a munition component of the same size, filled solely with the effective sensitive central plastic bonded explosive. This star-shaped configuration has no effect on the invulnerability which is maintained, while the degree of the fragmentation effect is improved, and while, according to certain alternative forms, everything behaves even as if the charge were made up completely of the effective central explosive.
It has also been found that such an improvement is also obtained when the sensitive and vulnerable central plastic bonded explosive is coated, along a star-shaped interface, not with a less sensitive plastic bonded explosive but with a pyrotechnic composition of the class of composite solid propellants which is still less sensitive and vulnerable than the least sensitive known plastic bonded explosives, sometimes referred to as "insensitive" ones.
This is all the more surprising, since this result, already surprising when all the charge detonates, is obtained while the pyrotechnic composition of the class of the composite solid propellants reacts without detonating.
This alternative form of the invention is all the more advantageous since it makes it possible at the same time to lower the vulnerability and to increase the fragmentation effect in comparison with the dual-composition component made of plastic bonded explosive of the abovementioned state of the art in the article "Insensitive munitions".